Pebble heater reactor



April 20, 1954 1.. c. BEARER 2,675,999

PEBBLE HEATER REACTOR Filed Dec. 19, 1952 INVENTOR.

IT. 0. BEARER ATTORNEYS Patented Apr. 20, 1954 PEBBLE HEATER REACTORLouis C. Bearer, Waco, Tex.,

a corporation of Delaware Petroleum Company,

assignor to Phillips Application December 19, 1952, Serial No. 326,995

6 Claims.

This invention relates to pebble heat exchangers. In one of its morespecific aspects, it relates to pebble heater reactors. In another ofits more specific aspects, it relates to means for introducing steam atthe top of the pebble heater reactor beneath the pebble inlet so as toprevent the contacting of hydrocarbon gas and the hot pebbles adjacentthe pebble inlet.

Heat exchangers of the so-called pebble heater type have been utilizedin recent years for the purpose of heating fluids to elevatedtemperatures. Such apparatus is especially suited for use in temperatureranges above those at which the best available high temperaturestructure alloys fail. Thus, such equipment may be used for superheatingsteam or other gases and for the pyrolysis of hydrocarbons to producevarious products such as ethylene and acetylene, as well as for otherreactions and purposes. Conventional pebble heater type apparatusincludes two refractory lined contacting chambers disposed one above theother and connected by a refractory lined passageway or pebble throat ofrelatively narrow cross-section.

Refractory solids of fiowable size and form called pebbles, are passedcontinuously and contiguously through the system, flowing by gravitythrough the uppermost chamber, the throat, and the lowermost chamber,and are then conveyed to the top of the uppermost chamber to completethe cycle.

Solid heat exchange material which is conventionally used in pebbleheater apparatus is generally called pebbles. The term pebbles as usedherein denotes any solid refractory material of fiowable size and form,having strength which is suitable to carry large amounts of heat fromthe pebble heating chamber to the gas heating chamber without rapiddeterioration or substantial breaking. Pebbles conventionally used inpebble heater apparatus are ordinarily substantially spherical in shapeand range from about inch to 1 inch in diameter. In a high temperatureprocess, pebbles having a diameter between about A; inch to inch arepreferred; The pebbles must be formed of a refractory material whichwill stand temperatures at least as high as the highest temperatureattained in the pebble heating chamber. The pebbles must also be capableof withstanding temperature changes within the apparatus. Refractorymaterial, such as metal alloys, ceramics, or other satisfactory materialmay be utilized to form such pebbles. Silicon carbide, alumina,periclase, beryllia, Stellite, zirconia, and mullite may besatisfactorily used to form such pebbles or may be used in admixturewith each other or with other materials. Pebbles formed of suchmaterials, when properly fired, serve-very well in high temperatures,some withstanding temperatures up to about 4000 F.

Pebbles which are used may be either inert or catalytic as used in anyselected process.

' The pebbles are heated in one of the chambers (preferably the upperone) by direct contact therein with hot gases, usually combustionproducts, to temperatures generally in the range of 1400" F. to 3200 F.The hot pebbles are thereafter contacted with the fluid to besuperheated or reacted, as the case may be, in the other chamber.Generally, the pebble inlet temperature in the lower chamber is about 50F. to about 2 0 F. below the highest temperature of the pebbles withinthe upper chamber. In processes for the production of ethylene fromlight hydrocarbons, such as ethane, propane, or butane, the pebbletemperature in the reaction chamber is usually in the range of 1200 F.to 1800 F. For the production of acetylene by pyrolysis of hydrocarbons,temperatures in the range of 1600 F. to 2000 F. are desirable.

In the past, considerable trouble has been encountered in that coke hasdeposited on the surface of the upper end of the reactor chamber andperiodically breaks loose and'gravitates through the reactor chamber,often depositing in the pebble outlet conduit or conduits, therebyresulting in the temporary slowing or stoppage of pebble flow throughthe reactor chamber and hence through the heating chamber. When thisoccurs the pebbles within the pebble heater chamber tend tobecomeoverheated and often fuse together, thereby causing considerable.maintenance difliculty. Under almost all operating conditions, aconsiderable portion of the gaseous reaction products obtained in thepebble heater reactor contact the hot pebbles from the heater chamberadjacent the entrance of those pebbles into the reactor. The gaseousproducts are overheated in the direct heat exchange and a considerableportion thereof is converted to coke within and on the reaction chamber.I have devised a means whereby the deposition of coke in the upper endof the reactor chamber is materially reduced.

- Each of the following objects of the invention is attained by at leastone aspect of this invention. An object of this invention is to providean improved pebble heater apparatus. Another object of the invention isto provide improved means for preventing the choking of pebble conduitsor elevator means bylarge coke aggregates.

point. A central core is providedin the reaction chamber so as to forman annular-pebble bed between the core and the outer shell of thereaction chamber. A water or=-steam conduit is passed upwardly throughthe central core and opens at the upper end portion of that core so asto permit the escape of steam from the upper end portion of thecore'into the hot pebble mass being discharged onto the top centralportion of the pebble bed. This blanket of steam prevents thehydrocarbon gases from contacting the hot pebbles beneaththe pebbleinlet conduit and prevents the overcrackmg'of those hydrocarbon gases inthat portion of the pebble bed. The steam which passes upwardly throughthe upper portion of the top section of the pebble bed, sweeps throughthe selectedportion of the pebble bedat the top of the reactor chamberthereby reducing the extent of contact of the incoming columnof hotpebbles and the hydrocarbon reaction products in that section of thepebble mass. The steam and reaction products are removed through agaseous effluent outlet conduit in the upper end of the reactionchamber. The central core may be provided so as to form the water orsteam conduit within its walls, thereby providing'means for convertingthe water tosteam or for superheating the steam before introductionthereof into the pebble mass.

Better understanding of this invention will be obtained upon study ofthe accompanying schematic win in h h:

Figure Us a diagrammatic representation of a reactor chamber of pebbleheater apparatus."

Figure 2 is a preferred modification of a. reactor chamber of pebbleheater apparatus of this invention. r

Figure 3 isaechematic view ofpebble heater apparatusof this invention.

Referring to particularly Figure lof the draw ings, reaction chamber IIcomprises elongated shell I2 closed at its upper and lower ends byclosure member I3 and I4, respectively. Pebble inlet conduit I5 extendscentrally in the upper end portion of that chamber and gaseous effiuentoutlet conduit, I5 extends upwardly from the upper end portion of thatchamber. Pebble outlet conduit I'I extends downwardly from the lower endof chamber II and reactant material inlet conduit I8 is connected to thelower end portion of chamber I'I through header member [9. A hollowcentral core 2I is provided within chamber I I'so as to extend upwardlythrough the lower portion thereof into the upper end portion of thatchamber. Perforate bafiie 22,- which is preferably suspended from theupper end portion of chamber I I by means of hanger members23 ispositioned directly below and concentrically with pebble inlet conduitI5. Bathe member 22 is positioned close enough to the upper endportionof central core 2| as to prevent pebbles frompassing between thetwomembers'and-into the in-'- terior of hollow core 2|. Bafile member 22is preferably perforate only in its upper end portion so as toconcentrate the flow of steam through and around the incoming column ofpebbles. Core 2| may be supported within chamber II in any one ofseveral difierent manners. Steam conduit 24 extends into the lower endportion of chamber II and upwardly to the interior of core 2I to theupper end portion thereof and opens into the interior of the hollow core2|.

Referring particularly to the device shown in Figure 2 of the drawings,parts like those described and discussed in connection with Figure l areidentified by like numerals. Core 25 extends upwardly irom thelower endportion of chamber II into the upper end portion of that chamber. Fluidconduit 26 extends into the lower end portion of chamber I I through thesupport for core 25' and passes helically upwardly through the wall ofcore 25 to the upper end portion of that core. A plurality ofperforations into the interior of core 25 at its upper end communicatesbetween the upper end portion of conduit 26 and the interior of core 25.Core 25-is provided with a closure member 30 in its lower end portion,clos-' ing the lower end portion thereof from the hollow core portionthereof above. A plurality of openings 21 extend through the lower endof core 25 below closure member 30 so as to permit the fiow of pebblestherethrough into pebble outlet conduit I'I. Bafile member 22 isclosedabout the upper end of core 25, "as shown in Figure -2. Such ajoining of the core and bafiie can also be used in connection withthe'device shown in Figur elr Pebble outlet Il may be in the former" aplurality of conduits extending from the annular chamber, if desired.

eferring particularly to the device shown in Figure 3 of the drawings,pebble heater chamber ZIifcomprises upright elongated shell 29 closedat-fits upper and lower'ends by closure members Hfand 32, respecti vely.Pebble inlet conduit '33 extends into theupper end portion of chamber 28and may be a single pebble "inlet conduit-centrall y positioned asshownin Figure 3 or alternatively may comprise a plurality of inletcon-- duits distributed over the upperend portion of chamber 28. Gaseouseffluent outlet-conduit 34 extends upwardly from the-upper end portionof chamber 28. Heatinggas inlet-means comprising inlet conduit 35 andheader member 36-is connected to thelower end portion of chamber 28,preferably bottom closure member 32.- Reactor chamber II comprisingupright elongated shell I2 closed at its upper and lower ends by closuremembers I3 and I4, directly below chamber 28 and pebble conduit I5 isconnected to the'lower end of chamber 28 and to the upper end oi'chamber II. Gaseous inlet conduit 3Iis connected to throat I5intermediate its ends, so as to provide for the introduction of an inertgastheretothus providing means for preventing the fiow of gaseousmaterials from one of the chambers to the other. Reaction material inletconduit I5 is connected to the lower end-portion of chamber II throughheader mem- Ga seous efiluent outlet conduit I6 ex-' tends upwardly fromthe upper end portion of chamber II. Fluid inlet conduit 24 extends intothe-lower end portion of chamber I I and extends upwardly throughthe-central core,-not shown, as discussed in connection with Figures 1and 2 of the drawing. Pebbleoutlet conduit Ii extends downwardly fromthe lower :end' of chamber II and is connected to the upper endportionof respectively, is positioned pebble entraining chamber 38. Pebbleentraining chamber 38 is closed about the lower end portion of elevatorconduit 39 and is provided with a lift gas inlet conduit 4I, which ispreferably coaxially disposed with respect to the lower end of elevatorconduit 39. I Elevator conduit 39 extends upwardly into lower endportion of gaspebble separator chamber 42. Gaseous eiiiuent outletconduit 43 extends from the upper end portion of chamber 42 and chamber42 is connected at its lower end to the upper end portion of pebbleinlet conduit 33. I v

In the operation of the devices shown in Figures l, 2 and 3 of thedrawings, pebbles are in-' troduced into the upper end portion of pebbleheater chamber 28 through pebble inlet conduit 33. The pebbles form acontiguous gravitating mass within that chamber and gravitate downwardlytherethrough. Gaseous heating material is introduced into the lower endportion of chamber 28 through inlet conduit 35 and header member 36. Thegaseous heating material may be a material that has been preheatedexternally of chamber 28 or may be a material which is burned in thelower end portion of chamber 28 in a gas distribution chamber, or may beburned on the surface of the pebbles within the chamber 28. In any case,the hot gaseous heat exchange material passes upwardly through thegravitating contiguous mass within that chamber, raising the pebbles toa desired temperature by direct heat exchange therewith. The gaseouseffluent is removed from the upper end portion of chamber 28 throughefiluent outlet conduit 34. Pebbles which have been raised to thedesired temperature within chamber 28 are gravitated from that chamberthrough pebble conduit I5 into the upper end portion of chamber I I.

The pebbles gravitating downwardly through conduit I 5 into the upperend portion of chamber II, are caused to pass over the surface ofperforate baflle member 22 and to divide into an annular mass of pebblesaround the baifie and around the central core formed within chamber I I.The pebbles form a contiguous gravitating mass within chamber II betweencore 2I or 25 and the shell I2. Reactant materials are introduced intothe lower end portion of chamber II through inlet conduit I8 and headermember I9. The reactant materials pass upwardly through the hotgravitating mass within that chamber being raised to reactiontemperature in a direct fheat exchange therewith. Resulting reactionproducts are removed from the upper end portion of the pebble mass inthe upper end of chamber I I and are removed from chamber I I throughaseous efliuent outlet conduit I6.

The pebbles cooled in the direct heat exchange with the reactantmaterials in chamber II are gravitated from the lower end portion ofthat chamber through pebble outlet conduit I 1. Those pebbles are passedinto pebble entraining chamber 38 wherein a stream of lift gas isintroduced through the mass of pebbles so as to entrain the pebbles andcarry them upwardly through elevated conduit 39 into gas-pebbleseparator chamber 42. In chamber 42, the velocity of the pebble flowlessens to such an extent that the pebbles are allowed to settle out ofthe gas stream, gravitating from the lower end of chamber 42 intochamber 28 through pebble inlet conduit 33. Gaseous eiiluent is removedfrom the upper end portion of gas-pebble separator chamber 42 to gaseouseiiluent outlet conduit 43.

Water or steam is introduced into the ch nt 6 berlI'I through conduit 24or through conduit 26'.

In the device shown in Figure 1 of the drawings, it is preferred tointroduce steam since conduit 2 24 is more insulated from the directrays of heat carried by the gravitating pebbles than is a conduit withinthe walls of the central core. In the device shown in Figure 2, steam orwater may be-introduced through conduit 26 and the water is converted tosteam during its passage upwardly through the walls of core 25 and thatsteam is introduced into the upper end portion of chamber I I. Steamwhich is introduced into the upper end-portion-of chamber from core 2Ior- 25 passes upwardly through perforate baffle 22 and through the thinlayer of pebbles formed thereon into and around the incoming column ofhot pebbles. This steam passing through the hottest portion of thepebble mass, substantially prevents hydrocarbon gases from contactingthose pebbles, thereby reducing the opportunity for those hydrocarbongases to become overcracked and to deposit carbonaceous materials aroundthe pebble inlet conduit and on the top end of the reactor chamber.After the steam has passed upwardly through the central mass of pebblescoming directly from the pebble inlet conduit, it passes across the topsurface of the reactor chamher and is removed from that chamber throughgaseous efliuent outlet conduit I6.

Inasmuch as the major deposition of coke in the reactor chamber isformed around the pebble inlet conduit, the exclusion of hydrocarbongases from that portion of the pebble mass materially reduces the cokedeposition in the upper end portion of the reaction chamber.

Various modifications of this invention will be apparent to thoseskilled in the art upon study of the accompanying disclosure. Suchmodifications are believed to be clearly within the skill of the art andwithin the spirit and the scope of this disclosure.

I claim:

1. An improved reactor comprising a closed, upright, elongated shell; apebble inlet conduit centrally disposed in the upper end of said shell;gaseous efliuent outlet means in the upper end portion of said shell;pebble outlet means in the lower end of said shell; a core, coaxiallydisposed within said shell extending upwardly from the lower end of saidshell and spaced below the upper end of said shell; gaseous materialinlet means in the lower end portion of said shell and communicatingwith the lower end portion of the annular chamber formed between saidshell and the said core; a baiiie, perforate in its central portion,disposed coaxially with respect to said pebble inlet conduit andpositioned so as to prevent pebble flow into said core; and an inert gasconduit means extending into said core and being open at the upper endof said core and below said perforate baflle.

2. The improved reactor of claim 1, wherein said perforate baille is aconical baiile closed around the upper 'end of said core, extendingupwardly to a point directly below said pebble inlet conduit and beingperforate only in its upper end portion.

3. The improved reactor of claim 2, wherein said pebble outlet means isa single outlet pebble conduit centrally disposed in the lower end ofsaid shell; and pebble outlet conduits extend through the wall of saidcore so as to provide communication between the annular chamber formedbetween said shell and said core and said pebble outlet conduit means.

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